Physiological and anatomical disturbances induced by chloride salts in sensitive and tolerant citrus: Beneficial and detrimental effects of cations

Abstract

In citrus, the relative contributions of chloride and cations to growth disturbances induced by salinity are a matter of controversy. Chloride salts (15 mol m-3 CaCl2, 30 mol m-3 CaCl and 30 mol m-3 KCl) reduced growth and gas exchange parameters, increased leaf damage and abscission and produced anatomical disarrangements and mineral imbalances in seedlings of sensitive Carrizo citrange (Citrus sinensis x Poncirus trifoliata) and tolerant Cleopatra mandarin (Citrus reshni). In both cultivars, Ca2+ was more beneficial, and K+ more detrimental, for growth than sodium. Photosynthesis and growth disturbances were highly correlated (P ≤ 0.001) with leaf Cl- build-up. In the sensitive genotype, Cl- was also significantly correlated with several leaf anatomical disarrangements, such as increase in succulence. In comparison with sodium, both calcium and potassium increased leaf Cl- content (up to 25 and 69%, respectively). Protective calcium effects were not linked to improvement of photosynthesis, reduction of leaf anatomical disarrangements, or prevention of Cl- and Na± increases. It is proposed that the ameliorative effects of calcium on citrus grown under salinity are mostly related to reduction of leaf abscission. Collectively, the data suggest a cause-effect relationship between Cl- build-up and reduced growth, whereas chloride correlations with declines in photosynthesis or increases in succulence appear to be indirect.